In manufacturing electronic devices, various processes are performed on an object to be processed. A thin film forming process is an example of such processes. A sputtering film forming apparatus is known as an apparatus for forming a thin film on an object to be processed.
For example, Japanese Patent Application Publication Nos. 2009-221595 and 2005-256112 disclose therein a sputtering film forming apparatus including a processing chamber, a stage, a plurality of targets and a plurality of shutters. In this film forming apparatus, the stage is provided in the processing chamber and rotatable about a central axis extending in a vertical direction while passing through the center of the stage. The targets are arranged above the stage along a circumferential direction. The shutters are provided between the stage and the targets and are rotatable independently. In the film forming apparatus disclosed in Japanese Patent Application Publication Nos. 2009-221595 and 2005-256112, a single target or two or more targets selected among the plurality of targets are exposed to the stage by rotating the plurality of shutters, and the target materials sputtered from the exposed targets are deposited on an object to be processed. The uniformity of the thin film formed on the object is improved by rotating the stage about the central axis when the target materials are deposited on the object.
However, there exists a device whose characteristics can be improved when forming a thin film in a state where the object is cooled to an extremely low temperature. A vertical magnetization-type MTJ (Magnetic Tunnel Junction) device used for a MRAM (Magnetoresistive Random Access Memory) or the like is an example of such device. The MTJ device includes two magnetic layers and a tunnel barrier layer disposed between the two magnetic layers. When such a MTJ device is manufactured, the tunnel barrier layer is formed on a first magnetic layer, and then, a second magnetic layer is formed on the tunnel barrier layer. The present inventors have found that the characteristics of the MTJ device can be improved by forming the second magnetic layer at an extremely low temperature.
Specifically, it has been found that the MTJ device having the second magnetic layer formed on the tunnel barrier layer at about −50° C. or below has high perpendicular magnetic anisotropy energy. The second magnetic layer formed at an extremely low temperature is considered as a high-quality thin film capable of improving the characteristics of the MTJ device.
In order to form a high-quality thin film, it is considered to transfer an object cooled by a cooling device into a film forming apparatus and form a thin film on the cooled object in the film forming apparatus. However, since the temperature of the object increases while it is being transferred from the cooling device to the film forming apparatus, the cooling effect to the object may decrease. In addition, since a process of transferring the object from the cooling device to the film forming apparatus is added, processing throughput decreases.